Powderless etching bath and method of etching



United States Patent 3,330,765 POWDERLESS ETCHIN G BATH AND METHOD OF ETCHING Clayton W. Hoornstra, Midland, Mich, assigncr to The Dow Chemical Company, Midland, Mich, a corporation of Delaware N0 Drawing. Filed Oct. 1, 1965, Ser. No. 492,258 7 Claims. (Cl. 25279.4)

This application is a continuation-in-part of a copending application Ser. No. 286,510, filed June 10, 1963, now abandoned.

The invention relates to an improved etching bath for powderless etching and the method of etching printing plates, name plates, templates and the like with the improved bath.

In the conventional method of making a metal printing surface, such as a photoengraving, a plate of an acid-soluble metal such as magnesium, zinc and their alloys is coated with a light-sensitive coating or enamel which is applied to the metal surface which is usually flat or cylindrical. The coated surface is exposed to light through a negative having an image thereon so as to produce a corresponding image in the coating. The exposed coating surface is developed forming an acid-resistant coating in the form of the image produced by the exposure. This acid-resistant coating is further hardened by heating and the image-bearing surface of the plate is then subjected to etching by an acid. As the etching proceeds, the acid tends to etch laterally and undercut the resist and thus distort the image. The standard method of preventing or reducing this undercutting at one time was to powder the plate, a time-consuming and difiicult operation. This method has now been replaced by the use of so-called powderless etching baths which provide for highly selective metal removal in considerable contrast to the uniform metal removal of metal sizing baths or the uniform minimal metal removal of pickling baths.

Heretofore, the acid constituent of powderless etching baths has consisted entirely, or almost entirely, of nitric acid. The use of such acid is accompanied by the evolution of irritating and toxic fumes. Attempts have been made to use hydrochloric acid but these have been largely limited to methods in which the powder method of reducing undercutting has been employed.

It is, therefore, a principal object of the present invention to provide an etching bath which does not produce irritating and toxic fumes during the etching process.

Another object of the invention is to provide a less expensive powderless etching bath than a bath employing nitric acid.

Another object of the invention is to provide a powderless etching method which permits avoiding the use of nitric acid.

A further object of the invention is to provide a suitable powderless etching bath employing hydrochloric acid as the etching agent.

These and other objects and advantages of the present invention will be more fully understood upon becoming familiar with the following description and the appended claims.

It has been discovered that upon combining 1) an etching agent consisting of hydrochloric acid with (2) an organic, Water-immiscible liquid comprising at least 65 percent by volume of a member of the group consisting of aromatic hydrocarbons and derivatives thereof having an aromatic nucleus and being predominantly aromatic in character, and mixtures thereof, and the balance, if any, being a water-immiscible orgnic solvent, said organic water immiscible liquid being substantially immiscible with water and substantially non-reactive with the etching agent and the metal to be etched, and with (3) one or 3,3393% Patented July 11, 1967 ice more filming agents selected from the group consisting of sulfonated or sulfated anionic surface active agents pos sessing solubility in both Water and the organic waterirnmiscible liquid employed, in concentrations hereinafter more particularly described, and (4) the balance being water, and the etching bath being maintained in an emulsified condition a powderless etching bath is provided which is suitable for photoengraving and for etching printing plates, name plates, templates and the like, which avoids the disadvantages of the nitric acid baths described above as well as the difiiculties encountered in prior attempts to use hydrochloric acid as the etching agent.

An organic compound that is predominantly aromatic in character exhibits the properties of a compound in which the characteristics of the resonant ring structure predominate, especially as to solvency behavior.

Suitable amounts of hydrochloric acid employed are here defined most conveniently in terms of the concentrated acid of commerce, although it is obvious larger volumes of more dilute aqueous acid containing corresponding weights of hydrogen chloride may be used. Concentrated hydrochloric acid consists of about 37.5 percent hydrogen chloride by weight. Operable amounts of hydrochloric acid range from 125 percent by volume of concentrated hydrochloric acid. A preferred range of hydrochloric acid concentration in the etching bath is from 7-15 percent by volume, in terms of the concentrated acid. If hydrochloric acid concentrations in the bath are too high, the etching rate becomes excessive and the area under the resist in photoengraving plates is poorly protected. If the concentration of hydrochloric acid is too low, not only does the etching rate become very slow, but there is a tendency for open areas to be subject to blank off, that is, the open area is not etched at all.

The organic, water-immiscible liquid may be a single compound or blend of such compounds. Required properties of this component of the bath are that it be substantially stable in the presence of dilute hydrochloric acid at bath temperatures, that it be a liquid at bath temperatures, and that it have some solvency for the surface ac tive agent. Substantially stable is defined as the non-occurrence of deterioration within a reasonable time period due to the presence of dilute hydrochloric acid which significantly alters the function of the organic Water-immiscible liquid Within the bath in an unfavorable manner.

The solvency properties of the organic, Water-immiscible liquid are further defined by requiring that at least 65 percent by volume, and more preferably at least percent, of such liquid is a member of the group consisting of aromatic hydrocarbons, derivatives thereof having an aromatic nucleus and being predominantly aromatic in character, and mixtures thereof, and up to 35 percent by volume, but preferably not more than 10 percent, of non-aromatic water-immiscible organic solvent.

Suitable aromatic hydrocarbons and derivatives of aromatic compounds when used as substantially pure compounds, and not as mixtures or blends, exhibit a boiling temperature in the range of about to about 735 F. In the case of mixtures of such compounds employed as the organic, water-immiscible liquid, the boiling temperature after distillation of about 10 percent by volume of the liquid is not appreciably below 195 F., while the boiling temperature after distilling off 90 percent by volume of the liquid should be below about 735 F.

Examples of suitable compounds include: diethyl benzenes, tetramethyl benzenes, diisopropyl benzenes, dodecyl benzenes, monochloroethyl benzene, diamyl naphthalene, and aliphatic naphthenics.

Non-aromatic organic solvents which may be used, but only as a part of the organic, water-immiscible liquid, are selected from organic liquids which are substantially immiscible with water, stable in the presence of aqueous a hydrochloric acid at bath temperatures, and liquid at bath temperatures. Preferably not more than about 10 percent by volume of such liquids is employed. In general, it is desirable to avoid alcohols and also aliphatics such as mineral seal oil or white mineral oil, though up to 10 percent of the organic, water-immiscible liquid may consist of such alcohol or high boiling parafiinic oil.

Suitable substantially non-aromatic solvents usable as a part of the organic, water-immiscible liquid include: hexyl acetate, trichloroethylene, ethylbutyl ketone, methylhexyl ketone, isophorone, d-limonene and turpentine. Generally, it may be said that water-immiscible, acid stable, non-aromatic esters, ketones, terpenes, isoparaffinic hydrocarbons boiling in the range of 200 to 500 F. and ethers may be so employed.

Certain commercial solvents also serve very effectively as the organic Water-immiscible liquid component of the bath. An example is a commercial aromatic solvent marketed under the tradename of Solvesso 150, which is a mixture of approximately 90 percent alkyl benzenes, 2 percent naphthalene and 8 percent naphthenes. It has a flash point of 150 R, an aniline point of 18 F., and a distillation temperature range at 760 mm. Hgzinitial boiling point of 303 F., 50 percent distilled at 378 F. and dry point at 415 F. Another commercial aromatic solvent suitably employed has the tradename Penola H.A.N. and contains 84 percent aromatics, has a flash point of 140 R, an aniline point of 2 F. and a distillation temperature range at 760 mm. Hgzinitial boiling point of 340 F., 50 percent distilled at 446 F. and dry point at 532 F.

Two additional commercial solvents found entirely satisfactory are Panasol AN1 and Panasol ANZ liquids. Both of these solvents consist of more than 90 percent by volume of aromatic hydrocarbons and derivatives thereof.

The amounts of the water-immiscible organic liquid employed may range from 1-10 percent by volume of the bath, but a preferred range is from 3-6 percent by volume.

The hydrophobic-hydrophilic filming agent employed is a compound or blend of compounds selected from the group consisting of sulfonated or sulfated anionic surface active agents possessing solubility in both water and the organic water-immiscible liquid employed in the bath. Suitable types of filming agents include the alkyl aryl sulfonates, esters of sulfosuccinic acid, chlorinated alkyl aryl sulfonates, alkyl aryl ether sulfonates, petroleum sulfonates, sulfonated fatty acid esters, sulfated castor oil or other sulfated natural oils and other surface active agents and mixtures thereof having the requisite solubility in both the organic water-immiscible liquid and water, and exhibiting the requisite filming properties. The filming agent employed must have a solubility, by weight, of at least 0.01 percent in each of water and the organic water-immiscible liquid, and further, must possess a solubility of at least 0.1 percent in at least one of water and the organic water-immiscible liquid. In addition, the filming agent must be entirely taken up between the two phases of the bath, with the preponderance of the filming agent being present in the oil phase of the bath. The suitable filming agents are further defined as having at least 10 carbon atoms in the hydrophobic portion of the molecule. The amounts of the hydrophobic-hydrophilic filming agent employed may range from 0.1 to 5 percent by weight of the bath, but a preferred range is from 0.3 to 4.5 percent by weight.

It is believed that in forming a film, the polar part of the filming molecule attaches to the metal surface while the hydrophobic non-polar segment of the molecule, having an affinity for the organic water-immiscible liquid, draws such atoms to it, thereby perfecting a substantially acid-resistant film. By virtue of the objects to be accomplished, the bath of this invention must have selective filming tendencies under the conditions present as the etching process is carried out, i.e., acid-resistant films must be formed and retained upon the side walls of the relief but adjacent resist-free areas must be susceptible to the etching action of the hydrochloric acid in a direction normal to the surface of the plate being etched.

Water constitutes the remaining essential component of the bath. It is to be noted, however, that in some baths there may be other materials present, particularly byproducts from the production of the foregoing components. Alternatively, other materials which enhance a particular effect may be employed.

Thus, in some instances, it has been found beneficial to add to the organic, water-immiscible liquid, as a modifier, a small amount of an ester such as n-hexylacetate. In other instances, it has been found quite beneficial to add small but very effective amounts of nitric acid in order to improve both the etching rate and the etch factor. The amounts of concentrated nitric acid (density 42 Baum) advantageously employed range from 2 to about 13 percent by volume based on the volume of concentrated hydrochloric acid employed, or, stated in other terms, from about 0.33 to about 2 percent by volume of concentrated nitric acid based on the total volume of the etching bath.

Etch factor as used in this specification is defined as the ratio of the depth of the etch adjacent to a line of resist divided by one-half of the total loss in width (i.e., side etch) of metal immediately beneath the resist.

In the practice of the present invention, it has been found desirable to impinge the bath upon the surface to be etched as by spraying, but much more preferably, by splashing. In the formulation of the etching bath, it has been found to be a general rule that as the concentration of the hydrochloric acid is increased within the aforementioned limitations, it is necessary to also increase the proportion of filming agent employed. It has also been found that the selection of the organic, water-immiscible liquid and of the filming agent are interrelated in that the filming agent must have some solubility in the organic water-immiscible liquid, as defined hereinabove. Due to bath depletion as the etching process is carried out, it is simpler and more convenient to designate amounts of components in terms of their initial concentrations.

Suitable metals which may be etched by this process include zinc, zinc-base alloys, magnesium and magnesiumbase alloy, all of which are substantially homogeneous metals suitable for photoengraving. A zinc-base alloy or magnesium-base alloy is defined as having at least percent of the base component.

The average bath temperature may be within a range from 50-120 F., but a preferred range is from 7090 F. A preferred embodiment of this invention comprises, per liter of bath, about ml. of 37.5 percent by weight hydrochloric acid, about 30 ml. of Solvesso aromatic solvent, about 5 grams of Ninex 300 triethanolamine dodecylbenzene sulfonate and about 15 ml. of 42 Baum nitric acid. The remainder of the mixture is water.

To carry out the etching process, it is preferred to employ an etching machine of the type disclosed in US. Patent 2,669,048, issued Feb. 16, 1954. In this Dowetch machine, rotating, elongated paddles intermittently splash the etching bath upwardly against the image-bearing surface of the object being etched. The splashing action of the paddles also serves to keep the bath in an emulsified state. The emulsified bath of this invention applied in the described manner for about 8 minutes will usually produce depths of etch from approximately 0.015 to 0.030 inch in line areas of the plate while generally producing proper depths in various other parts of the plate. Also, etch factors in line image areas from 20 to 40 are readily obtainable. It is obviously desirable to have as high etch factors as possible for faithful reproduction of the image in relief. However, it should be noted that the etch factor can be sensitive to changes in depth. Thus, etch factor should be considered as only one criterion of etching bath quality. The etching bath of the invention has very good chemical stability as a function of time and is capable of producing uniform and good results on consecutive plates over periods of many hours.

The following examples are intended to be merely illustrative of the invention and should not be construed as 5 limiting the scope of the invention.

In a series of tests employing the method and composi- TABLE I Surface Active Agent Test Range, 1111. M1. Typical Line No. Cone. Range, Solvesso HOl Etch Fac- Depth,

Name Nature or Identity w./w. percent 150 tor Range Mils (active ingradients) Tensol N Sulfonated Naphthalene Alkyl Ether 1-2 1 180-360 700 4-23 7-23 Sultrarm'n N Sodium Diamyl Naphthalene Sultanate 0.7 330 850 15-30+ 10-26 N inate 402 Calcium Dodecylbenzene Sul10nate 0. 4 240 900 12-24 12-24 Ninate 411 Amine Alkyl Aryl Sulionate 0.3 120 700 15 23 Aerosol OT-EG Mgthyll Heptyl Ester of Sodium Salt of Sult'osuccmic 0.8 180 950 23 16 c1 Alrowet D65 Dicctyl Sodium Suliosuccinate 0, 3 6 {Ninex 300 Triethanolamine Dodecylbenzene Sulfouate 0. 17 120-130 700 15-20 7 Stepan 164-16. Highly Sulfonated FattyAcid Ester plus Span 80 (Sorbil. 5 240 700 19 11 tan Monooleate) s ggggf fi f }Su1fated Castor on 540 850 7 1o 9 Triton 770 Sodium Salt of Alkyl Aryl Polyesther Sulfate 0. 1.0 240-300 700 8-19 9-12 1 60 ml. 11-hexyl acetate was added to the Solvesso 150 liquid.

tion of the invention, a powderless etching bath of 6 liters In an additional series of tests, small amounts of nitric volume was prepared in a miniature Dowetch machine 3 acid were employed in addition to hydrochloric acid.

by adding requisite quantities of concentrated aqueous hydrochloric acid (37.5 percent by weight HCl), an organic water-immiscible liquid, at surface active agent and water. The filming agent Was conveniently first dissolved or dispersed in a small amount of water before adding it to the resulting mixture in the bath. The bath temperature was The other conditions of the test were similar to those described for the first series of tests. The amounts of nitric acid and hydrochloric acid employed, the nature and amounts of surface active agent and the quantity of Solvesso 150 liquid employed, as well as the results obtained are summarized in Table II.

TABLE II Surface Active Agent Typical Test Range, ml. M1. M1. Etch Line No. Cone. Range, Solvesso HCl HNO; Factor Depth, Name Nature or Identity erceut 150 Added or Range Mils w. w. (active ingredients) 1 Ninex 300 Triethanolamiue Dodecylbenzene Sulfonate 0.5 180 700 30 30-50 17. 6

2 Ahcowet ANS Amyl Naphthalene Sodium Sultanate 2.4 570 900 20 22 16 3 Beaconal T Guanidine Salt of Monoethyl Phenyl Phenol 1.8 360 700 14.5 14.5

Monosulfonate. 4 Tndecyl Benzene Sull'onate .7 0.5 210 700 30-60 8-16 6 5 Aerosol O'I (E G)- Methyl Heptyl Ester of Sodium Salt of Sulfo- 2.0 300 950 120 24 18 succim'c Acid. r

Sodium Dodecyl Monochloro Diphenyl Oxide 4. 5 360 900 90 14.6 10

Sultanate.

Petroleum Sulfouate 1. 0-2. 5 250-310 950 30-90 6-30+ 9-21 Sodium Salt of Alkyl Aryl Polyet 0.7 300 700 30 10. 5 8 10"--. Tetranol Sodium Salt of Fatty Acid Ester 0.7 270 700 60 11.8 11.8

11 Trepanol S-301 Sodium Tridecyl Polyglycol Ether Sulfa 0.5 1 210 700 60 8 4 1 30 m1. n-hexylacetate added to Solvesso 150 liquid.

a light-sensitive polyvinyl alcohol resist thereon was exposed to a standard test pattern of letters, lines, dots and a halftone image, developed and descummed in the manner Well known to photoengravers. The plate was descummed by a 2-minute immersion in an aqueous solution consisting of 12 ounces per gallon of potassium hydroxide and 2 ounces per gallon of potassium permanganate, followed by brushing the surface with dilute nitric acid until the surface Was bright. The plate was then placed in the etching machine, the paddles were turned on and etching was allowed to continue for about 5 to 10 minutes.

In additional runs, made by way of comparison, a number of identical small magnesium photoengraving alloy test plates were prepared by photoprinting thereon both linework and halftone images with a polyvinyl alcoholchromate type resist by conventional processes. Just before use each plate was descummed by rubbing it vigorously with dry chalk. All etching was done in a miniature Dowetch machine wherein each plate was, in turn, mounted horizontally with the image side down and rotated in the splash emanating from the rotating paddles of the machine.

Three liters of 37.5 percent by weight hydrochloric acid and three liters of ordinary non-detergent type SAE 20 weight motor oil were placed in the machine and the paddles were run at 600 revolutions per minute (r.p.m.) for about one minute to form a composition outside the scope of the invention. We test plates were then etched at 7 a paddle speed of 600 r.p.m. with the bath at a temperature of 78 F.

The first plate was etched for 10 seconds. The reaction was violent. Image elements 0.009 inch wide or less were An additional series of tests was carried out to demonstrate the importance of maintaining the requisite proportion of aromatic solvent in the bath when employing non-aromatic solvent as part of the organic, water-imcompletely undermined by lateral etching and were lost miscible liquid. In each test there was employed a magthough the depth of relief was only 0.002 inch, indicating nesium alloy photoengraving test plate prepared as dean etch factor of less than 0.5. The results were comscribed in the foregoing comparison runs. Etching was pletely unsatisfactory. carried out in a miniature Dowetc machine having a The second plate was etched for 60 seconds. The etch bath volume of 6 liters and the bath being maintained at was 0.011 inch deep and the entire image was undermined 10 75 F. Tensol N surface active agent was employed as the and etched away, showing that the bath was completely filming agent in each test. Various amounts and proporunsuitable. ,tions of Enco Aromatic 150 solvent and Isopar L solvent 900 milliliters of 37.5 percent by weight hydrochloric within the scope of the invention were employed. acid and 240 milliliters of SAE 20 weight motor oil were Enco Aromatic 150 solvent is very similar to the Solvesplaced in a miniature etching machine and the balance of so solvent described hereinabove and consists of about the 6 liter bath was made up with water. The paddles 97.3 percent by volume of total aromatics. Isopar L were run at 600 r.p.m. for one minute before etching solvent consists of 99.6 percent by weight total saturates, was begun on magnesium test plates having a photoresist C isoparafiinic hydrocarbons being predominant, and image developed thereon. the balance being major amounts of C and C isopar- A first plate was etched for 6 minutes, while a second afiinic hydrocarbons. plate was etched for 90 seconds. Extremely rapid, sub By way of comparison, tests were run employing prostantially non-selective etching took place on both plates. portions of Enco Aromatic 150 solvents and Isopar L The foregoing bath was modified by the addition of outside the scope of the invention.

360 milliliters more SAE 20 weight motor oil, bringing The results of these tests are summarized in the followthe proportion of oil in the bath to 10 percent by volume. ing table.

TABLE III Enco Aromatic 150 Isopar L aliphatic olvent Solvent Ml. Tensol N Etch Line Etch Test No. 37.5% Filmer, Time, Depth, Factor Quality of Etch Percent Percent Percent Percent H01 grams Min. Mils v.[v. in v./v. total v./v. in v./v. total bath solvent bath solvent 6 75 2 25 700 172 3 17.5 9.5 Good. 5 75 2 25 700 215 9 15 s. 5 Do. 3 3o 2 20 700 215 12 19. 5 11.7 Do. 3 60 2 700 172 12 33. 5 1 No good, lost most of image. 6 75 2 25 600 172 13 25.5 22 Good. 6 s7 3 33 600 172 11 25. 5 5. 5 Do. 6 60 4 40 600 172 9 19 1 No good, lost most of image. 5 5 50 700 172 11 29 1 Do.

Percent v./v.=Percent volume by volume.

Total solvent=Total organic, water-immiscible liquid.

Ml.=Milliliters.

1=Less than 1.

The bath was mixed and a third plate was etched for 3 50 Various modifications may be made in the etching bath minutes at 74 F. The etch obtained was 0.016 inch deep. and method of applying such bath without departing All image elements less than 0.018 inch wide were comfrom the spirit of the invention and it is to be underpletely destroyed. Only large solid areas and large shadstood that the scope of the invention is limited only by ow tone areas survived at all. Such a bath, not according the appended claims as read in the light of the specificato the invention, was found completely unusuable for tion.

powderless etching. I claim:

A third bath was made up consisting of 420 milliliters 1. An emulsified powderless etching bath consisting of percent by weight hydrochlo ic acid and essentially of 1 to 25 percent by volume of 37.5 percent m1ll1l1ters of SAE 20 weight motor oil and sufiiclent by weight hydrochloric acid; 1 to 10 percent by volume water to bring the total volume to 6 liters. The paddles 60 of an organic, water-immiscible liquid; 0.1 to 5 percent of the etchingmachme were run throughout the test at by Weight of a hydrophobic-hydrophilic filming agent 600 r.p.m. while the bath was maintained at 76 F. A selected from the group consisting of sulfonated organic first magnesium telst plate was etched for 6 minutes to a compounds and sulfated Organic compounds; and the IA fi (1)?) f f SAE 20 g t balance being water; said organic, water-immiscible liqer m1 1 1 ers 0 W61 mo or 01 65 uid comprising at least 65 percent by volume of a memwas added to the bath and a second test plate was etched her of th e .group consisting of an aromatic hydrocarbon in 6 minutes to a depth of 0.014 inch. a derivative of n O h d b h Still an additional 120 milliliters of SAE 20 weight 1 Y T 9 motor oil was added to the bath and a third test plate m 1c nuc an bemg Predommanfly aromatlc char was etched for 6 minutes to a depth of 0.013 inch. w and mlxtufes f l and to 35 by '9 The three etched test plates were examined and were f a Y F f F organ": Solvent, sald Organic, found to be completely unsatisfactory. In each case image water'mlfmsclble llquld being Substantially Stable elements less than 0.012 inch wide were completely de- 111 the 831d bath at a temperature in the range of stroyed and only vestiges of image remained where there -r Substantially immiscible With the W (3) Su had been large solid and deep shadow tone areas. stantially non-reactive with the hydrochloric acid and 9 the metal to be etched, and (4) a liquid at bath temperatures; and said filming agent being further characterized as containing at least 10 carbon atoms in the hydrophobic portion of the molecule, and having a solubility, by weight, of at least 0.01 percent in each of the Water and the organic, Water-immiscible liquid.

2. An emulsified powderless etching bath consisting essentially of 1 to 25 percent by volume of 37.5 percent by weight hydrochloric acid; 1 to 10 percent by volume of an organic, water-immiscible liquid; 0.1 to percent by weight of a hydrophobic-hydrophilic filming agent selected from the group consisting of sulfonated organic compounds and sulfated organic compounds; and the balance being water; said organic, water-immiscible liquid comprising at least 90 percent by volume of a member of the group consisting of an aromatic hydrocarbon, a derivative of an aromatic hydrocarbon having an aromatic nucleus and being predominantly aromatic in character, and mixtures thereof, and up to percent by volume of a water-immiscible organic solvent, said organic, Water-immiscible liquid being (1) substantially stable in the said bath at a temperature in the range of 50120 F., (2) substantially immiscible with the water, (3) substantially non-reactive with the hydrochloric acid and the metal to be etched, and (4) a liquid at bath temperatures; and said filming agent being further characterized as containing at least 10 carbon atoms in the hydrophobic portion of the molecule, and having a solubility, by weight, of at least 0.01 percent in each of the water and the organic, Water-immiscible liquid.

3. An emulsified powderless etching bath consisting essentially of 7 to percent by volume of 37.5 percent by weight hydrochloric acid; 1 to 10 percent by volume of an organic, Water-immiscible liquid; 0.1 to 5 percent by weight of a hydrophobic-hydrophilic filming agent selected from the group consisting of sulfonated organic compounds and sufated organic compounds; and the balance being water; said organic, water-immiscible liquid comprising at least 65 percent by volume of a member of the group consisting of an aromatic hydrocarbon, a derivative of an aromatic hydrocarbon having an aromatic nucleus and being predominantly aromatic in character, and mixtures thereof, and up to 35 percent by volume of a water-immiscible organic solvent, said organic, Water-immiscible liquid being (1) substantially stable in the said bath at a temperature in the range of 50-120 F., (2) substantially immiscible with the water, (3) substantially non-reactive with the hydrochloric acid and the metal to be etched, and (4) a liquid at bath temperatures; and said filming agent being further characterized as containing at least 10 carbon atoms in the hydrophobic portion of the molecule, and having a solubility, by weight, of at least 0.01 percent in each of the water and the organic, water-immiscible liquid.

4. An emulsified powderless etching bath consisting essentially of 1 to 25 percent by volume of 37.5 percent by weight hydrochloric acid; from 0.33 to 2 percent by volume of 42 Baum nitric acid; 1 to 10 percent by volume of an organic, water-immiscible liquid; 0.1 to 5 percent by Weight of a hydrophobic-hydrophilic filming agent selected from the group consisting of sulfonated organic compounds and sulfated organic compounds; and the balance being Water; said organic, water-immiscible liquid comprising at least 65 percent by volume of a member of the group consisting of an aromatic hydrocarbon, a derivative of an aromatic hydrocarbon having an arcmatic nucleus and being predominantly aromatic in character, and mixtures thereof, and up to 35 percent by volume of a water-immiscible organic solvent, said organic, water-immiscible liquid being (1) substantially stable in the said bath at a temperature in the range of 50120 F., (2) substantially, immiscible with the water, (3) substantially non-reactive with the hydrochloric acid 10 and the metal to be etched, and (4) a liquid at bath temperatures; and said filming agent being further characterized as containing at least 10 carbon atoms in the hydrophobic portion of the molecule, and having a solubility, by weight, of at least 0.01 percent in each of the water and the organic, water-immiscible liquid.

5. An emulsified powderless etching bath consisting essentially of 7 to 15 percent by volume of 37.5 percent by weight hydrochloric acid; 3 to 6 percent by volume of an organic, water-immiscible liquid; 0.3 to 4.5 percent by weight of a hydrophobic-hydrophilic filming agent selected from the group consisting of sulfonated organic compounds and sulfated organic compounds; and the balance being water; said organic, water-immiscible liquid comprising at least percent by volume of a member of the group consisting of an aromatic hydrocarbon, a derivative of an aromatic hydrocarbon having an aromatic nucleus and being predominantly aromatic in character, and mixtures thereof, and up to 10 percent by volume of a water-immiscible organic solvent, said organic, water-immiscible liquid being (1) substantially stable in the said bath at a temperature in the range of 50-120 F., (2) substantially immiscible with the water, (3) substantially non-reactive with the hydrochloric acid and the metal to be etched, and (4) a liquid at bath temperatures; and said filming agent being further characterized as containing at least 10 carbon atoms in the hydrophobic portion of the molecule, and having a solubility, by weight, of at least 0.01 percent in each of the water and the organic, water-immiscible liquid.

6. A method of etching the surface of an acid-soluble metal plate having an acid-resistant, partial coating thereon, said metal being selected from the group consisting of zinc, zinc-base alloys, magnesium and magnesiumbase alloys which comprises; repeatedly impinging upon the metal surface to be etched an emulsified powderless etching bath consisting essentially of from 1 to 25 percent by volume of 37.5 percent by Weight hydrochloric acid; 1 to 10 percent by volume of an organic, water-immiscible liquid; 0.1 to 5 percent by weight of a hydrophobic-hydrophilic filming agent selected from the group consisting of sulfonated organic compounds and sulfated organic compounds; and the balance being water; said organic, water-immiscible liquid comprising at least 65 percent by volume of a member of the group consisting of an aromatic hydrocarbon, a derivative of an aromatic hydrocarbon having an aromatic nucleus and being predominantly aromatic in character, and mixtures thereof, and up to 35 percent by volume of a water-immiscible organic solvent, said organic, water-immiscible liquid being (1) substantially stable in the said bath at a temperature in the range of 50-120 F., (2) substantially immiscible with the Water, (3) substantially non-reactive with the hydrochloric acid and the metal to be etched, and (4) a liquid at bath temperatures; and said filming agent being further characterized as containing at least 10 carbon atoms in the hydrophobic portion of the molecule, and having a solubility, by weight, of at least 0.01 percent in each of the Water and the organic, waterimmiscible liquid.

7. A method of etching the surface of an acid-soluble metal plate having an acid-resistant, partial coating thereon, said metal being selected from the group consisting of zinc, zinc-base alloys, magnesium and magnesiumbase alloys which comprises: repeatedly impinging upon the metal surface to be etched an emulsified powderless etching bath consisting essentially of l to 25 percent by volume of 37.5 percent by weight hydrochloric acid; from 0.33 to 2 percent by volume of 42 Baum nitric acid; 1 to 10 percent by volume of an organic, waterimmiscible liquid; 0.1 to 5 percent by weight of a hydrophobic-hydrophilic filming agent selected from the group consisting of sulfonated organic compounds and sulfated organic compounds; and the balance being water; said organic, water-immiscible liquid comprising at least 65 percent by volume of a member of the group consisting of an aromatic hydrocarbon, a derivative of an aromatic hydrocarbon having an aromatic nucleus and being predominantly aromatic in character, and mixtures thereof, and up to 35 percent by volume of a water-immiscible organic solvent, said organic, water-immiscible liquid being (1) substantially stable in the said bath at a temperature in the range of 50-120 F., (2) substantially immiscible with the Water, (3) substantially non-reactive with the hydrochloric acid and the metal to be etched, and (4) a liquid at bath temperatures; and said filming agent being further characterized as containing at least 10 carbon atoms in the hydrophobic portion of the molecule, and having a solubility, by weight, of at least 0.01 percent in each of the water and the organic waterimmiscible liquid.

References Cited UNITED STATES PATENTS 7/1933 Hoy 252-792 X 3/1958 Hopkins et a1. 252-792 X 2/1962 Easley et a1 252-794 1/1963 Sherer et a1. 252-794 X 10/1963 Parkinson 156-14 6/1965 Gofiredo 252-792 X FOREIGN PATENTS 7/1957 Great Britain.

LEON D. ROSDOL, Primary Examiner. 15 ALBERT T. MEYERS, Examiner.

M. WEINBLA'IT, Assistant Examiner. 

1. AN EMULSIFIED POWDERLESS ETCHING BATH CONSISTING ESSENTIALLY OF 1 TO 25 PERCENT BY VOLUME OF 37.5 PERCENT BY WEIGHT HYDROCHLORIC ACID; 1 TO 10 PERCENT BY VOLUME OF AN ORGANIC, WATER-IMMISCIBLE LIQUID; 0.1 TO 5 PERCENT BY WEIGHT OF A HYDROPHOBIC-HYDROPHILIC FILMING AGENT SELECTED FROM THE GROUP CONSISTING OF SULFONATED ORGANIC COMPOUNDS AND SULFATED ORGANIC COMPOUNDS; AND THE BALANCE BEING WATER; SAID ORGANIC, WATER-IMMISCIBLE LIQUID COMPRISING AT LEAST 65 PERCENT BY VOLUME OF A MEMBER OF THE GROUP CONSISTING OF AN AROMATIC HYDROCARBON, A DERIVATIVE OF AN AROMATIC HYDROCARBON HAVING AN AROMATIC NUCLEUS AND BEING PREDOMINATLY AROMATIC IN CHARACTER, AND MIXTURES THEREOF, AND UP TO 35 PERCENT BY VOLUME OF A WATER-IMMISCIBLE ORGANIC SOLVENT, SAID ORGANIC, WATER-IMMISCIBLE LIQUID BEING (1) SUBSTANTIALLY STABLE IN THE SAID BATH AT AT TEMPERATURE IN THE RANGE OF 50-120* F., (2) SUBSTANTIALLY IMMISCIBLE WITH THE WATER (3) SUBSTANTIALLY NON-REACTIVE WITH THE HYDROCHLORIC ACID AND THE METAL TO BE ETCHED, AND (4) A LIQUID AT BATH TEMPERATURES; AND SAID FILMING AGENT BEING FURTHER CHARACTERIZED AS CONTAINING AT LEAST 10 CARBON ATOMS IN THE HYDROPHOBIC PORTION OF THE MOLECULE, AND HAVING A SOLUBILITY, BY WEIGHT, OF AT LEAST 0.01 PERCENT IN EACH OF THE WATER AND THE ORGANIC, WATER-IMMISCIBLE LIQUID. 